It is known to provide discharge openings in airbag modules through which the gas generated by a gas generator can escape from the airbag. This is desirable at the moment the vehicle occupant contacts the airbag. By the fact that the gas can escape through the discharge openings in a calculated way, the vehicle occupant is restrained in a controlled manner.
With such discharge openings it is, however, not desirable that gas can already escape through the discharge openings while the airbag is inflated, as this would require a larger gas generator to produce said additional gas volume. Therefore, various valves and tear seals for such discharge openings had been developed in the past. Such tear seals are, for example, known from U.S. Pat. No. 5,219,179. The discharge openings described therein are sealed by means of a cloth closure featuring a perforation or a tear seam along which the lid tears open thus releasing the discharge opening. With this embodiment it is obtained that the closure sealing the discharge opening tears open only at a specific internal pressure inside the airbag which occurs when the occupant impacts with the airbag. It is, however, a disadvantage of such a sealed discharge opening that a pressure increase inside the airbag, which tears open the lid, can already occur before the impact by the vehicle occupant. For example, vehicle occupant impacts with the airbag can occur when the airbag has already started to be deflated. Furthermore, not only an increased internal pressure in the airbag leads to tearing the lid sealing the discharge opening open, but also an increased force or tension in the airbag material in the circumference of the discharge opening can cause the lid sealing the discharge opening to be torn open. Such forces and tensions can, for example, already occur at the start of inflating the airbag. Altogether it is difficult with discharge openings sealed in this way to exactly set the starting time for discharging the gas from the airbag. This can have the consequence that the impact of the vehicle occupant on the airbag is not sufficiently absorbed or that the airbag is no longer sufficiently filled when the vehicle occupant bumps on the airbag. In both cases undesirable injuries of the vehicle occupant can be the result.